The investigations described will (1) isolate and examine individual central neurons responsive to noxious stimuli and (2) evaluate the effect(s) of analgesia-producing manipulations on their responsiveness. Glass micropipettes will be employed for purposes of extracellular unit recording in the trigeminal spinal nucleus, brain stem reticular core and diencephali areas of the brain. Noxious stimuli will include electrical tooth pulp and radial nerve stimulation and radiant heat. Analgesia-producing manipulations will include microiontophoretic morphine administration and focal electrical brain stimulation. These analgesia-producing treatments will be compared with non-analgesia producing treatments (e.g., chlorpromazine, pentobarbital,dextrorphan, etc. and non-analgesia-producing brain stimulation) and examined for effects on spontaneous unit activity and that evoked by peripheral noxious as well as non-noxious stimuli. The experiments will be performed in lightly anesthesized or decerebrated cats (primarily) or rats and in cats chronically implanted with stimulating electrodes (focal brain stimulation experiments). The objective of these investigations is to elaborate on the central site(s) and mechanisms of nociception and analgesia.